Method of manufacturing aluminum alloy articles

ABSTRACT

A method for making an article is disclosed. The method involves inputting a digital model of an article into an additive manufacturing apparatus comprising an energy source. The additive manufacturing apparatus applies energy from the energy source to successively applied incremental quantities of a powder to fuse the powder to form the article corresponding to the digital model. The powder includes an aluminum alloy having 2.00-10.00 wt. % cerium, 0.50-2.50 wt. % titanium, 0-3.00 wt. % nickel, 0-0.75 wt. % nitrogen, 0-0.05 wt. % other alloying elements, and the balance of aluminum, based on the total weight of the aluminum alloy.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a division of U.S. patent application Ser.No. 15/607,097, filed May 26, 2017, the entire contents of which areincorporated herein by reference.

BACKGROUND

This disclosure relates to additive manufacturing of aluminum articles.

Additive manufacturing technologies have been used and proposed for usefor fabricating various types of articles from various types ofmaterials. Broadly viewed, additive manufacturing can include anymanufacturing process that incrementally adds material to an assemblyduring fabrication, and has been around in one form or another for manyyears. Modern additive manufacturing techniques, however, have beenblended with three-dimensional computer imaging and modeling in varioustypes to produce shapes and physical features on articles that are notreadily produced with conventional molding, shaping, or machiningtechniques. Such techniques were initially developed using polymercompositions that are fusible or polymerizable in response to acontrollable source of light or radiation such as a laser.Three-dimensional articles can be fabricated a layer at a time based ondata from a corresponding layer of a three-dimensional computer model,which is generally known as stereolithography. With these techniques, apolymer powder or polymerizable liquid polymer composition is exposed toa source of energy such as a laser to fuse a thermoplastic polymerpowder by heating it to a fluid state or by initiating a reactionbetween components in a powder or polymerizable liquid composition. Thepowder or liquid can be applied a layer at a time by any known mechanismsuch as by spray or other application, but is often maintained in a bedwhere the article being fabricated is formed. After each layer is fusedand solidified, the article is lowered in the bed or the level of thebed is raised so that a layer of powder or liquid covers thepreviously-formed layer of the article, and another layer of the powderor liquid is fused and solidified by selective exposure to the energysource based on data from another corresponding layer of the computermodel.

Additive manufacturing techniques have also been used for thefabrication of metal articles. Metal thermal spray and other additivemanufacturing techniques for metals have of course been known for sometime. The application of stereolithographic manufacturing techniques tometals has led to significant advancements in the fabrication ofthree-dimensional metal articles. Using such techniques, a metal articlebeing manufactured is maintained in a bed of metal powder, with thesurface of the article below the surface of the powder in the bed sothat there is a layer of metal powder over the surface of the article.Metal powder in this layer is selectively fused such as by selectiveexposure to an energy source such as a laser or electron beam, accordingto data from a corresponding layer of a three-dimensional computer modelof the article. After each layer is fused and solidified, the article islowered in the bed or the level of the bed is raised so that a layer ofmetal powder covers the previously-formed layer of the article, andanother layer of the powder is fused and solidified by selectiveexposure to the energy source based on data from another correspondinglayer of the computer model. The resulting can be relatively complex,compared to structures obtainable by conventional metal fabricationtechniques such as casting, forging, and mechanical deformation.

Attempts to fabricate aluminum and aluminum alloy articles usingadditive manufacturing techniques have met with limited success.Aluminum alloys used for casting have been proposed or tried for powdercasting or additive manufacturing. However, many such alloys havelimitations on strength or other physical properties that renders themunsuitable for many applications, including but not limited to aerospaceand other applications requiring strength. For example, the alloyAlSi10Mg has been evaluated for additive manufacturing, but exhibitspoor ductility and fracture toughness. High-strength aluminum alloys arealso known. For example aluminum alloys 6061 and 7075 are well-known fortheir high strength in wrought aluminum articles. However, articlesformed from these alloys using additive manufacturing techniques aresusceptible to crack formation.

BRIEF DESCRIPTION

According to some aspects of the disclosure, a method for making anarticle comprises first generating a digital model of the article. Thedigital model is inputted into an additive manufacturing apparatuscomprising an energy source. The additive manufacturing apparatusapplies energy from the energy source to successively appliedincremental quantities of a powder to fuse the powder to form thearticle corresponding to the digital model. As described herein, thepowder comprises an aluminum alloy comprising 2.00-10.00 wt. % cerium,0.50-2.50 wt. % titanium, 0-3.00 wt. % nickel, 0-0.75 wt. % nitrogen,0-0.05 wt. % other alloying elements, and the balance of aluminum, basedon the total weight of the aluminum alloy.

In some aspects of the disclosure, the method also comprises selectivelyexposing incremental quantities of aluminum alloy powder in a layer of apowder bed over a support with a laser or electron beam to fuse theselectively exposed aluminum alloy powder in a pattern over the supportcorresponding to a layer of the digital model of the article. Then, themethod repeatedly: provides a layer of the powder over the selectivelyexposed layer and selectively exposes incremental quantities of aluminumalloy powder in the layer to fuse the selectively exposed aluminum alloypowder in a pattern corresponding to another layer of the digital modelof the article.

In some aspects of the disclosure, an aluminum alloy comprises 2-10 wt.% cerium, 0.50-2.50 wt. % titanium, 0-3.00 wt. % nickel, 0-0.75 wt. %nitrogen, 0-0.05 wt. % other alloying elements, and the balance ofaluminum, based on the total weight of the aluminum alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the disclosure is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe disclosure are apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

The FIGURE is a schematic depiction of an apparatus for making anarticle according to the methods described herein.

DETAILED DESCRIPTION

Referring now to the FIGURE, an example of an additive manufacturingsystem or apparatus 10 includes energy source 12 that generates anenergy beam 14, a first mirror or other optical guide 16, a secondmirror or optical guide 18, a frame 20, a powder supply 22, a powderprocessing bed 24, sintered powder material 26, a spreader 28, a powdersupply support 30, and a stack support 32. Of course, the illustrationin the FIGURE is schematic in nature, and many alternative designs ofadditive manufacturing devices are possible. Various types of additivemanufacturing materials, energy sources, and processes can be used tofabricate the air temperature sensor housing and the individual featuresthereof that are described herein. The type of additive manufacturingprocess used depends in part on the type of material out of which it isdesired to manufacture the sensor housing. In some embodiments, thesensor housing is made of metal, and a metal-forming additivemanufacturing process can be used. Such processes can include selectivelaser sintering (SLS) or direct metal laser sintering (DMLS), in which alayer of metal or metal alloy powder is applied to the workpiece beingfabricated and selectively sintered according to the digital model withheat energy from a directed laser beam. Another type of metal-formingprocess includes selective laser melting (SLM) or electron beam melting(EBM), in which heat energy provided by a directed laser or electronbeam is used to selectively melt (instead of sinter) the metal powder sothat it fuses as it cools and solidifies. The FIGURE merely illustratesone potential additive manufacturing system for creating an additivelymanufactured article.

Energy source 12 can be any source capable of creating focused energy.For example, energy source 12 can be a laser or an electron beamgenerator. Energy source 12 generates an energy beam 14, which is a beamof focused or focusable energy, such as a laser beam or an electronbeam. Optical guide 16 such as a mirror is present in some embodimentsto deflect radiation in a desired direction. A second optical guide 18,such as an optical head is present in some embodiments, and also directsenergy in a desired direction. For example, optical guide 18 can includea mirror and be attached to an x-y positioning device. Frame 20 is usedto contain powder material in powder supply 22 and in powder processingbed 24. Powder supply 22 and powder processing bed 24 include powdermaterial, such as or powdered metals. Powder processing bed 24 furtherincludes fused powder 26. Fused powder 26 is powder contained withinpowder processing bed 24 that has been at least partially sintered ormelted. Spreader 28 is a spreading device such as an air knife using aninert gas instead of air, which can transfer powder material from powdersupply 22 to powder processing bed 24. Powder supply support 30 andstack support 32 are used to raise and/or lower material thereon duringadditive manufacturing.

During operation, energy source 12 generates energy beam 14, which isdirected by the optical guides 16 and 18 to the powder processing bed24. The energy intensity and scanning rate and pattern of the energybeam 14 can be controlled to produce a desired result in the powderprocessing bed. In some aspects, the result can be partial melting ofpowder particles resulting in a fused structure after solidificationsuch as a sintered powder metal structure having some degree of porosityderived from the gap spaces between fused powder particles. In someaspects, the result from exposure to the energy beam 14 can be completelocalized melting and fluidization of the powder particles producing ametal article having a density approaching or equal to that of a castmetal article. In some aspects, the energy beam provides homogeneousmelting such that an examination of the manufactured articles can detectno particle pattern from the original particles. After each layer of theadditively manufactured article is completed, powder supply support 30is moved to raise the height of powder material supply 22 with respectto frame. Similarly, stack support 32 is moved to lower the height ofarticle with respect to frame 20. Spreader 28 transfers a layer ofpowder from powder supply 22 to powder processing bed 24. By repeatingthe process several times, an object may be constructed layer by layer.Components manufactured in this manner may be made as a single, solidcomponent, and are generally stronger if they contain a smallerpercentage of oxygen, hydrogen, or carbonaceous gases. Embodiments ofthe present invention reduce the quantity of impurities of, for example,oxygen, to less than 50 ppm, or even less than 20 ppm.

The digital models used in the practice of the disclosure are well-knownin the art, and do not require further detailed description here. Thedigital model can be generated from various types of computer aideddesign (CAD) software, and various formats are known, including but notlimited to SLT (standard tessellation language) files, AMF (additivemanufacturing format) files, PLY files, wavefront (.obj) files, andothers that can be open source or proprietary file formats.

As mentioned above, the powder used in the methods described hereincomprises an aluminum alloy. Aluminum alloys and techniques forpreparing them are well-known in the art as described, for example, inAluminum and Aluminum Alloys, ASM Specialty Handbook, J. R. Davis, ASMInternational, the disclosure of which is incorporated herein byreference in its entirety. Alloys can be formed by melting the basealloy elements in a crucible curing with rapid solidification, followedby cutting and grinding operations to form a metal powder. Particlesizes for the aluminum alloy powder can range from 10 μm to 100 μm. Insome aspects, the alloy elements can be combined together before forminga powder having a homogeneous composition. In some aspects, such asparticles will fully melt, one or more of the individual alloy elementscan have its own powder particles that are mixed with particles of otherelements in the alloy mixture, with formation of the actual alloy tooccur during the fusion step of the additive manufacturing process. Insome aspects, the powder is “neat”, i.e., it includes only particles ofthe alloy or alloy elements. In other aspects, the powder can includeother components such as polymer powder particles. In selectivesintering, polymer particles can help to temporarily bind metal powderparticles together during processing, to be later removed by pyrolysiscaused by the energy source or post-fabrication thermal processing. Insome embodiments, the article can be subjected to post-fabricationthermal processing such as solution heat treatment or precipitationaging to promote formation of phase particles such as intermetallicphase particles.

As mentioned above, the aluminum alloy described herein comprises2.00-10.00 wt. % cerium, 0.50-2.50 wt. % titanium, 0-3.00 wt. % nickel,0-0.75 wt. % nitrogen, 0-0.05 wt. % other alloying elements, and thebalance of aluminum, based on the total weight of the aluminum alloy.The other alloying elements can be selected among those known in the artfor use in aluminum alloys. In some embodiments, aluminum alloy elementscan form cerium-rich phase zones (also referred to in the metallurgicalfield as “particles”), which can help promote strength by inhibitingdislocation movement to resist deformation. In some embodiments, thepresence of nickel and titanium alloying metals can promote formation ofintermetallic phase particles comprising nickel, titanium, and aluminum.

In some, more specific, embodiments, the alloy can comprise ranges ofelements as specified below. In some embodiments, the alloy can comprise2.00-4.00 wt. % cerium, based on the total weight of the aluminum alloy.In some embodiments, the alloy can comprise 4.00-6.00 wt. % cerium,based on the total weight of the aluminum alloy. In some embodiments,the alloy can comprise 5.00-7.00 wt. % cerium, based on the total weightof the aluminum alloy. In some embodiments, the alloy can comprise8.00-10.00 wt. % cerium, based on the total weight of the aluminumalloy. In some embodiments, the alloy can comprise 0.50-1.50 wt. %titanium, based on the total weight of the aluminum alloy. In someembodiments, the alloy can comprise 1.50-2.50 wt. % titanium, based onthe total weight of the aluminum alloy. In some embodiments, thealuminum alloy can comprise nickel in an amount (i.e., greater than 0wt. % nickel) up to 3.00 wt. %, based on the total weight of thealuminum alloy. In some embodiments, the alloy can comprise 1.00-3.00wt. % nickel, based on the total weight of the aluminum alloy. In someembodiments, the alloy can comprise 0.25-0.75 wt. % nitrogen, based onthe total weight of the aluminum alloy. In some embodiments, the alloycan comprise 2.00-4.00 wt. % cerium and 0.50-1.00 wt. % titanium, basedon the total weight of the aluminum alloy. In some embodiments, thealloy can comprise 2.00-4.00 wt. % cerium and 1.50-2.50 wt. % titanium,based on the total weight of the aluminum alloy. In some embodiments,the alloy can comprise 5.00-7.00 wt. % cerium, 0.50-1.50 wt. % titanium,and 0.25-0.75 wt. % nitrogen, based on the total weight of the aluminumalloy. In some embodiments, the alloy can comprise 5.00-7.00 wt. %cerium, 1.50-2.50 wt. % titanium, and 0.25-0.75 wt. % nitrogen, based onthe total weight of the aluminum alloy. In some embodiments, the alloycan comprise 8-10 wt. % cerium and 0.50-1.50 wt. % titanium, based onthe total weight of the aluminum alloy. As mentioned above, otheralloying elements can be present in amounts of up to 0.05 wt. %, whichcan be any known in the art to be present in aluminum alloys. Examplesof other optional alloying or trace elements include, but not limitedto, manganese, zirconium, vanadium, and magnesium.

Examples of aluminum alloys according to the description herein includethose set forth in the Table below, with values provided as weightpercent and the balance being aluminum, and “others” including residualor tramp elements such as oxygen, sulfur, hydrogen, nitrogen, etc.:

TABLE Alloy # Ce Ti Ni N Other(s) 1 2.00-4.00 0.50-1.50 0.05 Max 24.00-6.00 1.50-2.50 0.05 Max 3  8.00-10.00 0.50-1.50 1.00-3.00 0.05 Max4 5.00-7.00 0.50-1.50 0.25-0.75 0.05 Max 5 5.00-7.00 1.50-2.50 0.25-0.750.05 Max

In some embodiments, alloys described herein can have a higher solidustemperature than common 6xxx series aluminum alloys as well as castaluminum alloys (e.g. C355.0 and C356.0). In some embodiments, alloysdescribed herein can have good weldability characteristics, which can bebeneficial for additive manufacturing processes. The disclosed alloyscan also provide good strength and other physical properties.

While the present disclosure has been described in detail in connectionwith only a limited number of embodiments, it should be readilyunderstood that the present disclosure is not limited to such disclosedembodiments. Rather, the present disclosure can be modified toincorporate any number of variations, alterations, substitutions orequivalent arrangements not heretofore described, but which arecommensurate with the spirit and scope of the present disclosure.Additionally, while various embodiments of the present disclosure havebeen described, it is to be understood that aspects of the presentdisclosure may include only some of the described embodiments.Accordingly, the present disclosure is not to be seen as limited by theforegoing description, but is only limited by the scope of the appendedclaims.

The invention claimed is:
 1. An aluminum alloy powder comprising greaterthan 2.00 and less than 4.00 wt. % cerium, 0.50-2.50 wt. % titanium,0-3.00 wt. % nickel, 0.25 to 0.75 wt. % nitrogen, 0-0.05 wt. % otheralloying elements, and the balance of aluminum, based on the totalweight of the aluminum alloy powder.
 2. The aluminum alloy powder ofclaim 1, wherein the aluminum alloy powder comprises 0.50-1.50 wt. %titanium, based on the total weight of the aluminum alloy powder.
 3. Thealuminum alloy powder of claim 1, wherein the aluminum alloy powdercomprises 1.50-2.50 wt. % titanium, based on the total weight of thealuminum alloy powder.
 4. The aluminum alloy powder of claim 1, whereinthe aluminum alloy powder comprises 1.00 wt % nickel, based on the totalweight of the aluminum alloy powder.
 5. The aluminum alloy powder ofclaim 1, wherein the aluminum alloy powder comprises 1.00-3.00 wt. %nickel, based on the total weight of the aluminum alloy powder.